Many engine installations require the use of a centrifugal compressor having an artifically extendable range. In particular, automotive engine applications exhibit cycle requirements demanding a "small" compressor at low speeds for good specific fuel consumption but a "large" compressor at full speed to meet peak power objectives. While it is known to use variable geometry diffusers to extend compressor range, such diffusers generally comprise multiple vanes that rotate between parallel endwalls to achieve throat area variations.